1. Field of the Invention
This invention relates to a suspend packet transmitter for transmitting suspend packets, specified in IEEE.
2. Description of the Related Art
IEEE in the United States of America has IEEE1394-1995 standard for packet communication since long ago and has IEEE1394a-2000 standard, revised above standard.
IEEE1394a-2000 standard specifies suspend function for setting a port in stand-by state to reduce electric power consumption and resume function for resetting a port from stand-by state. Other IEEE1394-1995 standard does not specify suspend and resume function.
In case of devices #1-#5, fulfilling IEEE1394a-2000 standard, connected together through port P3 and port P1 respectively as shown in FIG. 4A, when device #1 sends a suspend packet for port P1 of device #4 as shown in FIG. 4B1, the port P1 of the device #4 sends the suspend packet to device #3 and is set from active state to suspend state. When the device #3 receives a suspend signal, the device #3 sends a suspend signal to device #2 and all ports of device #3 is set from active state to suspend state. Thereafter, respective device sends a suspend signal in sequence and when the device #1 receives a suspend signal, port P3 of the device #1 is set from active state to suspend state.
When the device #1 sends a suspend packet for port P3 of the device #2 as shown in FIG. 4B2, the port P3 of the device #2 sends a suspend signal to device #3 and is set from active state to suspend state. Thereafter, respective device sends a suspend signal in sequence and when the last device #5 receives a suspend signal, port P1 of the device #5 is set from active state to suspend state.
When the device #1 sends a resume packet for port P3 of the device #3 as shown in FIG. 4C, the port P3 of the device #3 sends a resume signal to the device #4 and is set from suspend state to active state. Thereafter, respective device sends a resume signal in sequence and devices in order are set from suspend state to active state.
Objects to be Solved
If devices #3 shown in FIG. 4A fulfills IEEE1394-2000 standard, when device No. 1 sets port P1 of device #4 in suspend state, the device #1 sends a suspend packet to the port P1 of device #4. After the port P1 of device #4 receives the suspend packet, device #4 tries to set opposed port P3 of device #3 in suspend state. However, device #3 (fulfilling IEEE1394-2000 standard) does not work for suspend and resume function and then port 3 of the device #3 is not set in suspend state and only port 1 of device #4 is set in suspend state. Therefore, device #4 is disconnected with a communication network and then only devices #1-#3 are connected in the communication network.
When device #1 sets device #4 in resume state, the device #1 sends a resume packet to port P3 of device #3. However, device #3 does not fulfill suspend and resume function, so that device #3 can not set device #4 in resume state when the device #3 receives the packet. Therefore, device #1 can set device #4 in suspend state, but can not set device #4 in resume state.
There may be such problem when a device without suspend and resume function is connected between a device transmitting a suspend and a resume packet, and a device receiving the packet.
Therefore, an object of the invention is to provide a suspend packet transmitter for executing suspend and resume setting securely.